It uses infrared (IR) absorption as its detection method. IR absorption is but a subset of the overall field of “spectroscopy,” which measures the interaction of light and matter.

The basis of absorption spectroscopy is when an electromagnetic wave (i.e., the scientific description of “light”) with a particular wavelength impinges on a substance that absorbs a fraction of the total electromagnetic radiation. The wavelength of radiation is well known, for instance, in differentiating colors in the visible light spectrum.

In the infrared spectral region, the wavelength of light overlaps with discrete absorptions created by molecular vibrations. IR absorption is often used in diagnosing molecular composition based on “fingerprints” of these absorptions over a wide wavelength range. Conversely, if the strength of a single vibrational absorbance is known, a single wavelength is often used to determine the amount of a particular substance. This is how we measure moisture.